The aim of the proposed experiments is to study sociosexual behaviors (primarily aggression and sexual behavior) in the female hamster, focusing on developing our understanding of the cellular bases of hormone action on behavior. Experiments in the first section of the proposal are designed to determine the specific systemic hormone requirements for the female master's decline in aggressiveness and subsequent rise in sexual responsivity. It is expected that the inhibition of aggression will be estradiol sensitive, whereas sexual receptivity will require both estradiol and progesterone. Section II will examine neural sites of action of estradiol and progesterone in aggression and sexual behavior through the use of localized brain implants of estradiol or the synthetic progestin, R5020. A further dissociation of the hormonal control of aggression and sexual behavior may be related to different brain sites of action of these hormones. Based on the hypothesis that one action of steroid hormones on the brain is via the induction of neuronal protein synthesis, the experiments in Section III will investigate changes in neuronal ultrastructure, indicative of the level of protein synthesis, induced by systemic estradiol and progesterone. Ultrastructural changes in specific brain regions will be correlated with the behavioral state elicited by these hormone treatments. Correlations between sociosexual behaviors and neuronal ultrastructure will also be examined in cycling female hamsters. The role of neuronal protein synthesis in the hormonal activation of behavior will be examined in female hamsters receiving intracranial implants of the protein synthesis inhibitor, anisomycin (Section IV). The hypothesis that the behaviorally-relevant proteins are released by the Golgi complex will also be tested. In the final group of experiments (Section V), autoradiographic analyses of the location of estradiol- and progestin-concentrating cells in the brain and spinal cord of female hamsters will be aimed at 1) interpreting the effects of intracranial hormone treatment on behavior, and 2) assessing regional differences in the estradiol-induction of progestin receptors, a hypothesized regulatory step in progesterone's action on behavior. The value of studying cellular mechanisms of hormone action on an integrated behavioral system is emphasized. The significance of this research in the context of hormone regulation of neuronal plasticity is also considered.